1. Field of the Invention
The present invention relates to the fields of wireless communications, and more particularly, to a media access control method in a wireless network, which enables a plurality of devices to equally acquire a data transmission chance without competition in an unreserved transmission period.
2. Description of the Related Art
Recently, as applications such as wireless universal serial bus (USB), wireless display, and wireless video/HDTV streaming are integrated, high data transmission rates of several hundred Mbps are being required. In order to satisfy such a requirement, a variety of wireless communication standards capable of supporting high data transmission rates have been proposed. One of them is a WiMedia standard.
A channel access control method of the WiMedia standard is performed on the basis of competition such that a plurality of devices may use a slot period. In the channel access control method, different channel competition parameters are granted to application of four kinds of different access categories (ACs) including voice, video, best effort, and background, in order to perform differentiated transmission. That is, arbitrary inter-frame spaces (AIFS) may be granted differently, depending on the four categories to adjust a start time of backoff for carrier sense multiple access/collision avoidance (CSMA/CA). Furthermore, the ranges of the contention window (CW) determining the backoff time are granted differently in order to determine priorities in a channel occupation process of the CSMA/CA.
In particular, the conventional channel access control method of the WiMedia standard adopts a wireless channel access control scheme, in which a plurality of devices use an empty time slot on the basis of competition by using prioritized contention access (PCA) in an unreserved transmission period excluding a period reserved by a distributed reservation protocol (DRP), in a data transmission period of a super frame. This scheme is similar to an enhanced distributed coordination access (EDCA) scheme of existing IEEE 802.11e.
In general, when a time slot is reserved through a DRP period, a constant bit rate (CBR) type of traffic is transmitted. When this time slot is reserved, the time slot is not reserved in consideration of a maximum amount of data, but reserved in consideration of the average value for efficiency. At this time, when data is additionally generated, the reserved time slot period may become insufficient. In this case, traffic such as real-time traffic, which is sensitive of being transmitted after one super frame, needs to be transmitted by using the unreserved period (PCA period). Furthermore, video traffic having a variable bit rate (VBR) characteristic or file transfer protocol (FTP) traffic may use the PCA period, because it is not essential to transmit the traffic through a fixed time slot period. Furthermore, when VBR data is additionally generated or a command frame or control frame should immediately be sent to effectively change the communication, the PCA period is used. In the PCA period, however, the devices transmit data using the CSMA/CA. Therefore, periods in which a time slot is wasted by collision may increase, and the data transmission rate and the overall throughput may decrease.